SpecConstr: Properly create rules for call patterns representing partial applications

I think this is a reasonable approach to fix #21448 (closed)

Maybe we could put the void id always at the front (not just in specConstr) and get rid of addVoidWorkerArgSpec

But it seems likely that some places in the compiler still assume tyVars come first (e.g #21449) so likely not worth changing both things at once and risking more breakage.